docs: def _find_hstreaming():
      """Finds the whole path to the hadoop streaming jar.
  
      If the environmental var HADOOP_HOME is specified, then start the search
      from there.
  
      Returns:
          Full path to the hadoop streaming jar if found, else return an empty
          string.
      """
      global WARNED_HADOOP_HOME, HADOOP_STREAMING_PATH_CACHE
      if HADOOP_STREAMING_PATH_CACHE:
          return HADOOP_STREAMING_PATH_CACHE
      try:
          search_root = os.environ['HADOOP_HOME']
      except KeyError:
          search_root = '/'
      cmd = 'find %s -name hadoop*streaming*.jar' % (search_root)
      p = subprocess.Popen(cmd.split(), stdout=subprocess.PIPE,
                           stderr=subprocess.PIPE)
      HADOOP_STREAMING_PATH_CACHE = p.communicate()[0].split('\n')[0]
      if search_root == '/' and not WARNED_HADOOP_HOME:
          WARNED_HADOOP_HOME = True
          hadoop_home = HADOOP_STREAMING_PATH_CACHE[:HADOOP_STREAMING_PATH_CACHE.rfind('/contrib/')]
          logging.warn('Set the HADOOP_HOME environmental variable to your hadoop path to improve performance. Put the following [export HADOOP_HOME="%s"] in ~/.bashrc' % hadoop_home)
      return HADOOP_STREAMING_PATH_CACHE